(1) Field of the Invention
This invention relates to a motor control apparatus for a hybrid vehicle, and more particularly to control of a motor upon compulsory regeneration of a filter which collects fine particles in exhaust gas.
(2) Description of the Related Art
Conventionally, a hybrid vehicle or a hybrid electric automobile wherein an internal combustion engine (engine) and an electric motor (motor) are used in combination to obtain driving force for the vehicle has been developed and placed into practical use. As hybrid vehicles of the type described, a series hybrid vehicle wherein an engine is used exclusively for an electric power supplying source (generator) for a motor and a parallel hybrid vehicle wherein an output power shaft of an engine and an output power shaft of a motor are mechanically connected to each other such that a driving wheel is driven by driving force of both of the engine and the motor are known.
In the parallel hybrid vehicle, a driving toque requirement is determined from load information such as an operation amount of the accelerator pedal by the driver and the speed of rotation of the engine, and the output power distribution between the engine and the motor is set from the remaining capacity (charging rate) of the battery.
Incidentally, it is a possible idea to apply a diesel engine as the engine for a parallel hybrid vehicle. In particular, a technique is know wherein an oxidation catalyst (DOC) and a filter for particulate collection are interposed in an exhaust path of a diesel engine such that PM (Particulate Matter) included in the exhaust gas is collected by the filter and the PM collected by the filter is oxidized (burned) to continuously regenerate the filter. It is to be noted that, in the following description, the PM is used in the same meaning as soot.
In such a technique as described above, for example, a pressure difference sensor is provided for detecting the pressure difference between the entrance and the exit of the filter, and if the pressure difference detected by the pressure difference sensor becomes equal to or higher than a predetermined value, it is determined that the filter suffers from clogging, and compulsory regeneration of the filter is executed.
Upon such compulsory regeneration, additional fuel injection (post fuel injection) is performed at a later stage of the expansion stroke or at an initial stage of the exhaust stroke. Thus, from within the additional fuel, unburned fuel (HC: hydrocarbons) undergoes oxidation reaction (combustion) by an oxidation catalyst so that the temperature of exhaust gas flowing into the filter is raised by heat of the reaction then. Thus, the temperature of the exhaust gas flowing into the filter is raised so high that the PM in the filter is self ignited and burned thereby to achieve compulsory regeneration of the filter (first prior art).
It is to be noted that Japanese Patent Laid-Open No. 2001-115869 (hereinafter referred to as Patent Document 1) discloses a technique wherein, in a hybrid automobile which has an ordinary traveling mode in which the automobile travels while changeover between traveling by an engine and traveling by a motor is performed suitably and a special traveling mode in which the automobile travels while being driven only by the engine, when the catalyst is not in an activated state, the traveling mode of the automobile is compulsorily changed over to the special traveling mode. By the control described, when the temperature of the catalyst is low, the catalyst temperature can be raised rapidly (second prior art).
Incidentally, in the parallel hybrid vehicle, when the remaining capacity of the battery becomes low, the motor is sometimes driven by the engine so that it acts as a generator to charge the battery.
However, the first prior art described above has a subject that, if charging of the battery while the vehicle is in a stopping state (such charging is hereinafter referred to as stopping vehicle generation control or merely as generation control) and compulsory regeneration of the filer overlap with each other, then since the oxygen is consumed by the combustion of the fuel, the compulsory regeneration is not promoted and the compulsory regeneration time period is elongated, resulting in deterioration of the fuel cost. In particular, when the motor is driven by the engine and acts as a generator, the load to the engine increases and the fuel injection amount increases while the excess air ratio decreases (that is, becomes rich) and almost all of the oxygen is used for the combustion. Therefore, the oxygen concentration in the exhaust gas drops and the oxygen amount to be supplied to the filter decreases, and the combustion (oxidation) of the PM in the filter is not promoted and the compulsory regeneration time period is elongated. Then, the fuel cost is deteriorated as the compulsory regeneration time period is elongated.
Meanwhile, according to the technique disclosed in Patent Document 1 (second prior art), when the catalyst is not in an activated state, the traveling mode is compulsorily changed over to the special traveling mode in which only the engine is used for traveling of the vehicle. However, the second prior art is a technique which is applied while the vehicle is traveling, but a countermeasure for solving the subject described above which arises while the vehicle is in a stopping state is not disclosed at all.